1. Field of the Invention
This invention relates in general to a method and apparatus for dispensing objects. In particular, the invention relates to a method and apparatus for injecting spherical sealer balls into an oil well.
2. Description of the Prior Art
When an oil or gas well is completed, it is common practice to cement the well casing into the well. The casing is then perforated to allow fluid from the producing formations to flow into the well bore.
In order to increase the productivity of oil and gas wells, producing formations are sometimes treated by hydraulic fracturing and acidizing. Hydraulic treating fluid is pumped into the well bore and exits through the perforations in the casing into the formation.
If some of the perforations are blocked by sediment, or if part of a formation has a lower permeability, part of the formation may not be treated. To ensure that this does not happen, perforation sealer balls are introduced into the treating fluid. The sealer balls seal the open perforations, thus forcing the treating fluid to flow through the other perforations.
Several different types of methods and devices have been devised for injecting sealer balls into a well. These devices must be capable of withstanding the high pressures of the well bore. The devices must also be able to easily and accurately count the number of balls inserted into the well. Sometimes several hundred balls are used, so it is sometimes very difficult to keep up with how many balls have been inserted.
Some prior art ball injectors resemble heavy duty gum ball machines, with complicated mechanisms. The complexity of such machines make them expensive to manufacture and difficult to use and to maintain.
U.S. Pat. No. 3,715,055 (Kendrick et al.) shows a ball injector which has a housing, a rotatable shaft having a helical rib, and a sleeve having a spiral groove. The groove and the rib have different pitches, so they form separate compartments in which the balls are carried. As the shaft is rotated, the balls are forced downward out of the housing. The device is loaded by inverting the housing, dropping balls into the outlet, and rotating the shaft in the opposite direction.
U.S. Pat. No. 4,111,334 (Winn, Jr., et al.) shows a similar ball injector. This device has a housing, a stationary shaft having a spiral groove, and a rotatable sleeve having a helical rib. The sleeve is rotated to move the balls along the shaft. The device is loaded by inserting balls into the top of the device and rotating the sleeve in the normal direction.
Although these devices perform their intended function, the spiral groove makes them expensive to manufacture. It would also be desirable to be able to load the devices more quickly, and to have a simple way to keep a count of the number of balls which have been loaded.